Apparatus for conditioning mixtures of granular solids and liquid for centrifuging



.Iuly 13, 1937. G. E. STEVENS APPARATUS FOR CONDITIONING MIXTURES OFGRANULAR SOLIDS AND LIQUID FOR CENTRIFUGING Original Filed April l. 19523 sheets-sheet `1 NDD WQfy L INVENTOR. G. e van s ATTORNEY.

July 13, 1937. G. E. STEVENS 2,086,951

` 'APPARATUS FOR CONDITIONING MIXTURES OF GRANULAR V SOLIDS `AND LIQUIDFOR CENTRIFUGING original Filed April 1, 1952 s sheetssheet 2 L I X@ Q sN s u Ns f5 V Lg Q Y INVENTOR. 6.5.5even5 BY Y 1 n (I l ATTORNEY.

July 13, 1937. a E. STEVENS 2,086,951

` APPARATUS FQR CONDITIONING MIXTURES GRANULAR SOLIDS AND LIQUID FORGENTRIF'UGING:`

Original Filed ApriLl.' 19:52 3 sheets-sheet :s r

ATTORNEY.

i Patented July 13, 1937` l Y 7 UNITED STATES PATENT i OFI-ICE APPARATUSFOB CONDITIONING MIX- TURES OF GRANULAR SOLIDS AND LIQ FOR CENTRIFUGINGl George E. Stevens, Scottsbluff, Nebr., assignor to Western StatesMachine Company, Salt Lake City, Utah, a corporation of Utah y Originalapplications April 1, 1932, Serial No. Y 602,621, and May 12, 1934,Serial No. 725,404.

l Divided and this application December 4. 1934,

Serial No. '156,003

5 claims. (ci. 12v-i7) I This invention relateslto apparatus forcondihighly supersaturated and ready for further tioning mixtures ofgranular solids and liquid for treatmentin a, crystallizer. The objectof this i A centrifuging, such as sugar massecuites and `furthertreatment is to cause the greatest possible i i i magmas, `and isintended to solve certain probprecipitation of sugar from solution intosolid i 5 lems that have long been a source of much trouble grains orcrystals of as nearlyuniiorm' size as 5 l and heavy loss in themanufacture of sugar and practicable. The crystallizers are`substantially l similar materials. horizontal drums provided withinternal `stirrers 1 For purposes of illustration the invention isthrough which coolwater is circulated in" order l described as appliedto the manufacture of sugar gradually to cool the low grade massecuitefrom l in beet factories,` although it is' equally advanthe vacuum panand cause additional crystals to 10 `tageous in the production of canesugar. In the be Vprecipitated therefrom. i i usual beet factory, afterthe sugar-containing Treatment in the crystallizers is usually con-Juice extracted from sliced sugar beetshas been tinued over a period offrom 40 to 60 hoursvin subjected to boiling, filtering, andconcentration order toobtain the optimum yield of sugar. 1It l5 andcrystallization in a vacuum pan, the mass ofV results in the productionof massecuite which is 15 sugar grains mingled with a considerableamount "verystiff and viscous due not only to the precipiof motherliquor (which t mixture y is termed a tation of sugar crystals but tothe congelation oi massecuite) is subjected to centrifuging andcolloidal constituents which tendl tobecome set washing incentrifugalsof the ltering type in or non-fluid at low temperatures.order to obtain relatively pure sugar 4grains and For propercentrifuglng massecuite must ow 20 to collect the `mother liquorseparately. `A batreadily enough to permit it to build up quickly intery or group of several centrifugal machines is an evenring around theinside of the centrifugal o usually arranged below a common overheadmixbasket and to permit proper separation of mother lng tank whichsupplies charges of massecuite to `liquor and sugar grains. Two of theimportant the centrifugals through discharge chutes, or factors aiectingthe uidity of the massecuite are 25 goosenecks, leading from the bottomof the its liquid content andits temperature. YThe lack tank. A t t offluidity characterizing low grade massecuite The centrifugally extractedsyrup or mother from a crystallizer has always been a source of liquor,called green liquor, and the wash syrup much trouble to the sugarmaker.If he chills produced by thepassage of wash water "through themassecuite to'the low temperatures that are 30 sugar in a. centrifugalare conducted to separate necessary to recover the maximum amount ofstorage tanks, 4while the sugar grains retained sugarrb'ycrystallization. a Stiff and ViSeouS mass in the centrifugal aredischarged therefrom, cori-V iS obtained Which Cannot be centrifugedSatisveyed to a granulator for drying, and subse- `-factori1y; if hedrops the massecuite from the` quently packaged. The green liquors andwash crystallizer while still fairly hot a great deal of 35 SYI'uDSStill `contain a largelenough sugar content the available crystalformation is sacriced and in solution to make its recovery a valuableand t0 e Corresponding extent Sugar iS left in Solution important itemin sugar manufacture, and the and 10st in the nalmolaSSeS.

40 recovery of part of this dissolved sugar consti- For many years DaStVarious attempts to Solve 4o tutes what is known as the .raw side"operation this problem have been made. Heat jacketing of in sugarmanufactureA as distinguished from the themixlng tenlv for the Purpose0f Circulating hot white side operation briefly referred to above. Wateralongthe bottom of the tank has been tried. In` beet sugar manufacture,centrifugally exbut without success `because the conduction of tractedliquorsy that hold in solution much less heat to the mass of material inthetank is so than'i)` percent. of dry matter are not considered slowthat the temperature cannot be raised sub- 45 worth reprocessing andareusually sold as final stantially unless the heating fluid is hot enoughto molasses for cattle feed .or the like.` In cane melt and redissolveand even caramelize the sugar manufacture the liquors may be reworkedsugarv contacting the jacketed portion of the tank, economically down toa dry substance content of thus involving a much greater loss than gain.50

` vabout 40 percent. In each case when further re- Partial reheating ofthe cooled massecuite in the covery of sugar from low grade liquors ismade crystallizer by circulating hot water through the thesugar-containing liquors or syrups are subcrystallizer'cooling devicealso has been tried, but Jected to filtration. evaporation, and boilingin `this gained no advantage-quite the contrary, in

vacuum pans until the resulting massecuite is fact-because to achieveany appreciable reheat- 56 ing high temperatures must be used for aconsiderable period of time, and the entire mass of material must beheated, with unavoidable remelting and possibly caramelization of sugar,before the batch can be run off through the centrifugals. Moreover, thispractice permits the massecuite to cool during passage from thecrystallizers to the centrifugals, which may occupy a period of morethan an hour for some of the charges withdrawn from the mixing tank, andcooling destroys any advantage that might have been realized from thepreceding reheating operation.

Another expedient frequently tried out in prior practice is to add hotmolasses or syrup to the massecuite in the mixing tank. This not onlycauses redissolution and melting of sugar grain but also adds heavily tothe work imposed upon the centrifugals so that additional centrifugalapparatus and operatorsI are required, thus entailing a heavy'extraexpense for which there is no compensating advantage. The mostsatisfactory expedient, and the one commonly used prior to the presentinvention, is to add cold water to the massecuite in the mixing tank.The cold water increases fluidity without remelting or caramelizing thesugar grains, but it redissolves a large amount of sugar and addsmaterially to the volume of material that must be run through thecentrifugals.

The present invention solves this heretofore unsolved problem byproviding improved apparatus for conditioning massecuites, magmas andlike mixtures just before introduction into centrifugals,-apparatuswhich operatesin such manner as substantially to eliminate remelting,cara-melization and redissolution of the sugar grain while at the sametime conditioning the material for easy and relatively quickcentrifuging without increasing the volume of material to becentrifuged.

The improved apparatus in general comprises a mixing tank having in thebottom portion thereof a movable heat-transferring stirrer which ismaintained at a proper temperature by the circulation of hot liquidtherethrough and which is arranged to impart dry heat to a regulatedstream of massecuite in an amount sufficient to render the massecuitefluent and in optimum condition for centrifuging.

The heat-transferring stirrer of the invention preferably presentseffective heat-conducting surface of not less than one square foot foreach cubic foot of the portion of material being stirred by it in thebottom portion of the mixing tank. In the embodiment of the inventionillustrated in the drawings as the preferred form for use in theconditioning of massecuite dropped from crystallizers, the stirrer isconstructed as a rotatable heating coil, with convolutions of the coilarranged to keep uniform the consistency of material adjacent thereto,and means are provided for delivering massecuite to the coil in a streamsubstantially equal to the flow of messecuite through the dischargechutes of the tank into the centrifugals. Thus the massecuite iscontinuously and uniformly conditioned and then centrifuged, until theentire supply of massecuite in the tank is exhausted.

The present application is divisional of my copending application,Serial No. 725,404, led May 12, 1934, and is also divisional of myco-pending application, Serial No. 602,621, led April 1, 1932. Subjectmatter shown and described but not claimed in this application, has beenclaimed in the aforementioned applications.

In the accompanying drawings, which illustrate preferred embodiments ofthe invention for the conditioning of low grade sugar massecuites,

Figure 1 represents a diagrammatic side elevation of a sugar plantarrangement system including crystallizcrs, the improved hot minglersand centrifugals,

Figure 2, a diagrammatic end view thereof,

Figure 3 represents a fragmentary vertical cross sectional view of a hotmingler tank of the type diagrammatically illustrated in Figure 1,

Figure 4, a section along the line 4-4, Figure 3,

Figure 5, a section along the line 5-5, Figure 3,

Figure 6, an enlarged fragmentary side view of a spiral coil of a hotmingler of the type shown in Figure 3, the coil functioning as theheating and stirring element for reducing the viscosity of themassecuite,

Figure 7, a sectional view of a modification of the tank and coilarrangement, and

Figure 8 is a section taken along the line 8--8, Figure 7.

In the drawings, in the several views of which like parts have beensimilarly designated, the crystallizers indicated by the referencenumeral 9 are shown in an elevated position and are provided withoutlets IO through which material passes by gravity into a hot minglertank I2, the o lower portion of which has convergent front and rearwalls. Extending transversely of the tank I2 is a deck I3 provided withopenings I4, controlled by gates I5 in operative connection with leversI6.

Extending through the tank is a hollow shaft I'I carrying a pulley I8,which may be connected with any suitable driving element (not shown) torotate the shaft. Spiral coils I9 and 20 eccentrically placed on theshaft are in fluid-conducting connection therewith, and it willbeobserved that the coils are staggered as to their direction of Winding,the coils I9 winding to the left, and the coils 20 winding to the right.This staggered arrangement prevents the massecuite from ow- 4 crease theeffective heating surface, add, to the r agitating action of the coilsas well as providing bracing elements therefor.

The circulating system for the above apparatus comprises a storage* tank23 which receives boiling waterfrom a conveniently located boiler orother source, by means of a conduit 24. A temperature regulator 25thermostatically adjusts a valve 26 and thereby regulates the supply ofhot water to the tank 23 in accordance with a predetermined temperatureof the water in the tank. The tank is provided with an overflow outlet21.

Water from tank 23 is circulated through the heating coils I9 and 2|] bymeans of a duplex pump 28, operatively connected with a motor 29. Thewater is drawn from tank 23 through a pipe 30 and then passes through aconduit 3| into the hollow shaft I'I. After circulating through thecoils, the water enters return conduit 32 and again enters tank 23.

In carrying out the present invention, the massecuite is dropped fromthe crystallizers onto the deck I3 of the hot mingler tank I2, and therate at which the massecuite passes through the openings may beregulated by adjustment of the gates I5 through the medium of levers I6.The

lll)

massecuite on entering the tank I2 is at once subjected to the actionlof the coils I9 and 20.

Since one of the dominant features of the present invention is to reducethe viscosity of the massecuite without dissolving any appreciableamounttof sugar, `the time during which the massecuite is subjected tothe action .of the moving coils, and the temperature to which themassecuite is heated must be carefully. controlled,

The area of the moving heating surface is taken as a constant, and thenthe time factor is adjusted, depending upon the temperature of themassecuite entering the hot mingler tank, the density of the massecuite,the rate of movement of the heat transferring surface and thetemperature of the circulating medium.

'Ihe present invention departs from the prior art in providing for arelatively large heating surface, preferably a moving heating surface,for contacting massecuite just before it. enters a centrifugal and whileit is not desired to be limited to any specific ratio of heating surfaceto volume of massecuite, satisfactory results are obtained by providingat least one square foot of moving heating surface per cubic foot ofmassecuite when it is desired to `have a, relatively low temperaturedifference between the heating ,medium and the massecuite. t b

In other words, the ratio of heating surface to volume of massecuitemust be adjusted, together with the temperature difference `so that` themassecuite can pass through the hot mingler and be reheatedto a suitabletemperature in a relatively short time. Thus, little re-dissolving ofcrystals is encountered, while at the `same `time the viscosity of themassecuite is reduced to a point where it can be readily spun in thecentrifugals. b b b In accordance with the present invention, there isemployed a heating medium at a temperature only slightly higher than thefinal temperature "of the heated massecuite. `Although water` is thepreferred heating medium, other fiuids may be used. It is ofconsiderable importance to use a moving` heating surfacehaving atemperature from 50 to 65C. or slightlyhigher than theheated massecuite,since temperatures of C. to 55 C. ar `the highest that massecuite can bereheate without dissolving an appreciable portion of the sugar crystals.By `the continuous contact of the moving heating surfaces and theiragitationl of the material, the temperature of vthe massecuite bodybeing subjected to the moving surfaces can be raised a number of degreesC. in

, a time interval of only a few minutes.

The heating; coils I9 and 20 are preferably maintained at a temperaturevarying between C. and C., when the temperature' of the massecuiteentering the hot mingler tank I2 is about 30s C. The massecuite is thenheated to a temperature varying between 40 C. and 50'."v C., by thecontinuous application of dry heat.

Under the-"conditions above set forth, it takes approximately one andfive-tenths seconds to" raise the temperature of one hundred pounds ofmassecuite 1 C., and approximately twenty-two seconds `to raise onehundred pounds of massecuite 15. C., orl a range of five to ten minutesto raise 'one ton oftV massecuite 15 C.,` `The time factor depends uponthe temperature of the massecuite enteringthe tank, the density of themassecuite, the. temperaturel of the circulating heating fluid, the rateof movement of the heating` surfaceand the square feet of moving heatingsurface, the latter remaining a constant.

tion of the material is another factor influencing the beneficialresults. The material upon dischargingfrom the hot mingler'tank can bereadily spun in the centrifugals, and since it isin an ,undilutedcondition an increase of at least 15 to 20 per cent in centrifugalcapacity results from 4 the treatment.

The above explanation `discloses that there is a correlation ofl threefactors, namely, the time factor, the ratio of effective heating surfaceto the volume of massecuite in the tank, and a low temperaturedifference between the re-heated massecuite and the heating medium.

In an actual operation, 124,360 pounds of heating fluid at a temperatureof 60 C. were required each hour to transmit the necessary heat to themassecuite. Stated differently, approximately 450,000 Bft. u. per hourwere required to heat 30,000 pounds of low grade beet sugar massecuitepassing through the hot mingler tank per hour. Using water at atemperature of 60 C., 1040 B.,t. u. were required per square foot'ofmoving heating surface. 40B.` t. u. per degree difference in temperatureper square foot of heating surface per hour gave satisfactory results.

When the crystallizers 9 are ready to drop, the auxiliary mechanism ofthe system is started and the temperature regulator 25 adjusted to thedesired temperature. Hot water-is then circulated through the system,including the coils I9 and 20 until the system is well heated. Thecrystallizer 9 is then opened and the massecuite is allowed to flow ontothe deck I3 in the hot mingler tank I2. After the deck I3 is wellcovered, all the gates I5 are opened a notch or two and the massecuiteis distributed over the coils I9 and 20.

. tice is employed.

Massecuite passing through goosenecks 22 drops directly intocentrifugals 33. While a gravity ow system has been illustrated, it isto be understood that the hot mingler tank is adapted for use-in anytype of factory arrangement, and when the crystallizers 9 are disposedat a lower elevation than the centrifugals 33 and the mat terial pumpedto the centrifugals, the tank may be installed adjacent the centrifugalsat any convenient point between the crystallizers and the centrifugalswithout impairing its efficiency.

` In the modification illustrated in Figures 7 ACf) and 8, massecuitedropped from the crystallizers 9 is directed onto a chute 34 supportedon the upper edge of tank i2.

A primary heating and agitating element 35 and a secondary heating andagitating element 36 of the system are disposed one above the other inthe tank l2, which, in the operation, is a part of the secondaryelement.

The primary element comprises a tank 31, the walls of which are doubledto provide a water jacket 38. In the lower part of the tank, a shaft 39of a rotary agitator 40 extends lengthwise thereof substantially in theaxis of the circle of the rounded bottom of the tank.

The shaft 39 is mounted in bearings 4| and 42, three of which aresupported on cross beams 43 adjacent the ends of the tank, and one ofwhich is at a median point of the tank, supported on a cross beam 44.The portions 45 of the shaft extending through the bearings 4I andthrough the ends of the tank, are hollow and con-` nected with the bodypart 39 of the shaft by means of flanged couplings 46.

Tubular stirrers 41 on thehaft, of U-shaped form, have arms 48 whichproject radially from the shaft in connection with its hollowend-portions 45. These rotating stirrers operate to simultaneouslyagitate and heat the material in the tank in the manner hereinbeforedescribed. Stufnng boxes 49 are provided at the ends of the shaft toprovide a fluid-tight connection between the pipes of the fluidcirculating system and the hollow portion 45,0f the shaft.

The main parts of the U-shaped stirrers, extending parallel to theshaft, are provided with scrapers 50, to wipe the surface of the tank atthe inside of its jacket, for the purpose of presenting a clean surfacefor the ready transference of heat from the heating-fluid in the jacketto the material in the tank. The scrapers also aid in preventing anyoverheating of massecuite by reason of its remaining too long in contactwith the water-jacketed surfaces.

The arms 40 are preferably arranged in pairs of unequal lengths, so thatthe parts of the stirrers extending parallel to the shaft, are atunequal distances from the axis of rotation of the same. In this manner,the stirring and heating element covers a wide area in its rotarymovement and thoroughly agitates and heats the material Within saidarea, by the movement of the stirrers in intersecting zones.

An agitator constructed similarly to that of the first describedheating-element has its axis of rotation coincident with the axis of thecircular bottom portion of the tank l2. The agitator, like that of theheating element 35 comprises a shaft 5I, the end portions of which aresupported in bearings on cross beams 52.

U-shaped tubular radial stirrers 53 are connected with the hollow endportions of the shaft 5| in a circulating system of the same characteras that previously described. Scrapers 54 on the body parts of thestirrers, extending lengthwise of the tank, in parallel relation to theshaft, are provided to wipe the surface of the lower portion of thetank, the wall of which is doubled to provide a water jacket 55.

The tank 31 of the primary heatingelement has an overflow 56, the levelof which may be varied by adjustment of a vertically movable gate 51.The gate has to this end a screwthreaded stem 58 projecting through anopening of a. support 5S erected upon the edge of the tank, and it isprovided with a nut 60 bearing upon the support.

It will be understood that water circulation through the Water jackets38 and 55 and through the stirrers 41 and 53, is effected in the samesystem as that disclosed in Figure 1, each of the aforementionedelements being provided withinlet and outlet connections in a mannerwell known in the art. The circulation of the heating fluid through thejackets and agitators is effected at a predetermined and automaticallyregulated temperature.

Likewise, if desired, each element may be provided with its owncirculating system and subject to individual temperature control.

When massecuite is fed from the crystallizers onto the chute 34, itenters the primary element and is at once subjected to agitation by therotary stirrers 41.

The rotary movement of the agitator 41 keeps the material in the tank 31in motion while it is being heated by the hot water constantlycirculated through the agitator and through the jacket of the tank. TheScrapers wipe the heating surface of the tank to constantly present aclean surface. It will be understood thatthe temperatures of the heatingmediums are only slightly higher than the temperature of the enteringmassecuite to avoid a harmful increase in the temperature of thematerial.

The heated massecuite overflows from the primary tank 31 into tank I2across the properly adjusted gate 51, and is then subjected to a secondheating influence combined with an agltation action, by the heatingfluid constantly circulated through agitator 53 and the jacket 55 and bythe rotary movement of the agitator. The temperature of the heatingmediums is preferably higher at this stage of the treatment, but onlyslightly in excess of the temperatures of the massecuite passing throughthe goosenecks 22.

It is to be understood that whenever it is desired to regulate the rateof discharge from the tank, the goosenecks may be valve-controlled.

In the preferred form of the present invention, there is no need todilute the massecuite during or after crystallization, the treatment bymeans of moving contact with dry heat Within the body of massecuitebeing sufficient to readily reduce the viscosity of the massecuite, eventhough abnormally low temperatures have been used in the crystallizer's.

Since there is no increase in volume and a decrease in viscosity, thecentrifugals operate at maximum capacity and with an improved yield ofsugar per cycle, and the sugar obtained from the centrifugals may be ofhigher quality. These results mean substantial increases in theelficiency of sugar faqtory operation.

It is desired to point out that a dual action is effected in the heatingoperation. The massecuite moves through the coils or stirrers on its wayfrom inlet to outlet, and at the same time the coils and stirrers aremoved through the massecuite. In this way a relatively large volume ofmassecuite contacts each heating surface in a given period of time.

An example of the effectiveness of apparatus constructed in accordancewith this invention in commercial operation is furnished by thefollowing record from oneof the beet sugar factories in which it hasbeen installed. This factory during its last campaign had an average of44 crystal lizer hours for each 1150 cubic feet, or 107,000 pounds, ofmassecuite, during which period of time the temperature of themassecuite was lowered from C. to 30 C. It spun 22,379 tons of rawmassecuite in 66.65 slicing days, or an average of 335.8 tons per day,or approximately 14 tons per hour.

` fterthe operatlonof the mingler became con-` tinuous at-the start oi:`the campaign, the masse-l cuite flowed through the gates in the deckofthe i mixingtank as rapidlyas it` was drawnoi` into s reached thegoosenecks it had been raised from C. to 44 C., in the average time'ofabout seven minutes, which was the average timeof one spin-` ning ycycleof the centifugals. Water `at s an average temperature of- 57` C. wasused to maintain the temperature ofthe mingler.`

the material The, average `dry substance of entering the crystallizerwas 90.0, andthe average `dry` substance ,leaving the' crystallizer was89.8. Small amounts of lcold Water were introducedinto the massecuite inthe crystallizers,

which accounts `for the `fractional difference in dry substance. Therewas no dilution of the `massecuite after leaving the crystallizers, andthe percentage of dry substance, or density, of themassecuite as spunwas the same as when leaving Raw massecuite contains gums, colloids,etc.,

f which upon cooling tend to jelliiy and become Very viscuous orsemi-solid. i; Dry heat and agitation has the propertypf breaking upthis` viscosity and rendering the material more uent, `much more so thanthe addition of cold water or For this reason, the apparatus of `myinvention permitsthe boiling of lower purity raw pans to obtain thelowest possible molasses purity, since the subsequent treatment inthemixer of the resulting toughf massecuite readily s conditions it foreffective treatment in the centrifugals. ,l

It is to be understood that variations in the l construction andarrangement in the elements of the `system and the parts of theapparatus ineluded therein may be 'made within the scopez of theinvention. Also it is to be understood that if Scrapers of the typeshownin Figures 'l and 8 are desired, in la device of the typeillustrated in Figure 3, they may be mounted on the coils I9 and 20, l i

While the foregoing description has pointed out that the hot mingler isparticularly adapted for the treatment of massecuite passing from thecrystallizers to the centriiugals,` it is to be understood that theapparatus may be effectively employed in other treatments in the sugarman-` ufacturing process and elsewhere, as at the affini ation stationof a sugar refinery and in the conditioning of massecuites which passfrom a vacuum pan to centriiugals without intermediate treatment incrystallizers.

For example, it maybe used to great advantage in connection with thewhite mixer for controlling the temperature and viscosity of whitemassecute after it is dropped from a Vacuum pan and during thecentrifuging of the entire batch of massecuite. As a result of suchtreatment a bettercontrol ofthe ash and moisture content in the whitesugar is obtained, and sugar of a more uniformy quality and better coloris thereby produced. The continuous, `uniform high uidity of massecuiteconditioned in this manner greatly increases the capacity of thecentriiugals without loss of sugar grain by dissolution, caramelizationor remelting.

The foregoing data as to temperatures, etc., relate to actual operationson the raw side of a beet sugar factory. Since white cane sugarmassecuite, for example, is capable of withstanding lhighertemperatures` without injury than low grade massecuite, it will beunderstood by sugar engineersand operators that the temperatures `usedin :conditioning this and other mixtures of granular solids, such assugar, and liquids, such as syrup, may be varied in accordance withqualities of the mixture to be centrifuged. i i i What I claim anddesire to secure by Letters Patent is:

lower portion of the tank from the upper portion thereof, controllablegates for regulating the iiow of` material from the upper to the lowerportion of the tank, means for circulating i hot iiuid through saidstirrer, and means for maintaining the uid circulating through thestirrer at a temperature not `materially above the nal temperature ofthe conditioned material adjacent the delivery passages, the circulatingmeans havingcapacity to supply alarge enough flow of hot fluid to imparta uniform temperature to successive portions of the material flowingpast the stirrer without substantial drop in temperature of the fluid socirculating.

of sugar `grains and syrup, the combination of a mixing tank forming areceptacle for the mixture to be conditioned and centrifuged, the bottomportion of the tank having outlet passages for delivering theconditioned material directly to individual centrifugals, an internallyheated tubular stirrer revolubly mounted in the lower portion of thetank adjacent said outlet passages, means for forcing, a circulation ofhot fluid through said stirrer while it is revolving, means formaintaining the hot fluid supply at a temperature not harmiully abovethe maximum temperature to be imparted to the mixture near the outletpassages, the hot fluid circulating means and stirrer being dimensionedto maintain a 4flow of hot fluid of large enough volume to transfer therequired heat to the portion of the mixture being stirred withoutsubstantial drop in the temperature of the hot fluid passing through thestirrer.

3. In an apparatus for conditioning a mixture of sugar grains andsyrup,- the combination with a mixing tank forming a receptacle for themix- 2. In an apparatus for conditioning a mixture sioned to expose atleast one square foot of heattransferring surface for each cubic foot ofthat portion of the mixture being stirred by it at a time, and means forcontinuously circulating through the stirrer a supply of hot uid at apredetermined temperature not harmfully above the maximum temperaturemixture.

to be imparted to the 4. In a sugar centrifugal apparatus comprising acentrifugal separator and a mixing tank whose discharge outlet leadsdirectly to the centrifugal, a partition partly dividing said tank intoi communicating compartments, a tubular internally heated stirrerrevolubly mounted in each compartment for heating in successive stages astream of massecuite flowing through the compartments into successivecontact with the stir- 0 rers therein, means for forcing a continuousflow of hot fluid through said tubular stirrers, and

means for maintaining the temperature of the` hot fluid owing throughthe stirrers not harmfully above the maximum temperature which it 5 isdesired to impart to the massecuite as it enters the discharge outlet.

5. Apparatus for conditioning a mixture of v sugar grains and syrup forimmediate centrifuging comprising, in combination, a mixing tank l0forming a receptacle for mixture to be conditloned and centrifuged, thebottom portion of the tank having outlet passages for delivering theconditioned material directly to individual centrifugals, an internallylheated tubular stirrer providing at least one square foot of heatingsurface for each cubic foot of mixture being stirred revolubly mountedin the lower portion of the tank adjacent said outlet passages, meansfor forcing a circulation of hot fluid through said stirrer While it isrevolving, means for maintaining'the hot iiuid supply at a temperaturenot harmfully above the maximum temperature to be imparted to themixture near the outlet passages, the hot uid circulating means andstirrer being dimensioned to maintain a ow of hot iiuid of large enoughvolume to transfer the required heat to the portion of the mixture beingstirred Without substantial drop in the temperature of the iluid passingthrough the stirrer.

GEORGE E. STEVENS.

